The goal of this project is to understand the molecular basis for the normal development of the vertebrate inner ear. Our major accomplishment this year was the characterization of the inner ears of mice with the Otx1 gene deleted. Otx1 gene is one of the murine orthologues of the Orthodenticle gene in Drosophila. Otx1 encodes for a transcription factor that is highly conserved among species. The deletion of Otx1 gene in mice resulted in malformations of the brain and the inner ear. The gross anatomical development of the mutant inner ears was analyzed using a paint-filling technique. In addition, the location of each presumptive sensory organ in the otocysts of Otx1 mutant mice was analyzed using molecular markers. Results from these studies showed that Otx1 is important for the formation of the lateral canal and ampulla. The development and the final positioning of some of the sensory organs in the inner ear were also affected in the absence of the Otx1 gene. These experimental approaches can be broadly applied for the analysis of other mutant inner ears derived from spontaneous mutations or specific gene targeting. In addition, in collaboration with Eric Green in NHGRI, we have characterized the expression of Pendrin (PDS) in the developing mouse inner ear. PDS has been recently identified to be the gene responsible for the most common form of syndromic deafness, Pendred syndrome. Gene expression studies showed that PDS transcripts are restricted to nonsensory regions of the developing mouse inner ear. These PDS-expressing areas most likely serve to maintain fluid homeostasis within the inner ear. The role of PDS in maintaining fluid homeostasis as well as the etiology of the Pendred syndrome will continue to be investigated using mouse models. Other ongoing projects in the laboratory include investigating the function of BMP4 in inner ear development, and gene expression studies in both chicken and mouse inner ears. - inner ear development, gene expression, avian retroviral vectors, chicken embryos, retinoic acid, lunatic fringe, bone morphogenetic protein